Hydraulic pump assembly

ABSTRACT

A hydraulic pump assembly comprises a rotatable piston drum (20) with at least one centrifugal lever (23) pivotally attached thereto for radial movements between radial flanges (20′) under the action of centrifugal force at rotation of the piston drum. The centrifugal lever (23) is arranged to control the position of a valve member, preferably a ball (22), at the opening end of a bore (21) in the piston drum (20). There is a defined friction surface (28; 32) between the lever (23) and one of the radial flanges (20′), and there are spring means (29-31; 25, 33) for resiliently biasing the lever against said one of the flanges.

This application claims the benefit of Swedish Application No. 1350384-2filed Mar. 26, 2013 and PCT Application No. SE2014/050168 filed Feb. 11,2014.

TECHNICAL FIELD

The present invention relates to a hydraulic pump assembly, comprising arotatable piston drum with at least one centrifugal lever pivotallyattached thereto for radial movements between radial flanges under theaction of centrifugal force at rotation of the piston drum, thecentrifugal lever being arranged to control the position of a valvemember, preferably a ball, at the opening end of a bore in the pistondrum.

BACKGROUND OF THE INVENTION

Such a hydraulic pump assembly can be used in a system including a wetdisc coupling for distributing torque between front and rear axles of anall wheel drive vehicle (AWD) and/or between left and right wheels of atwo or four wheel drive vehicle. This hydraulic pump assembly foractuating a wet disc coupling is shown and described in WO 2010/019094and in a more developed form in WO 2011/043722. For a betterunderstanding of the background of the invention, reference is made tothese two publications, especially the latter.

A desirable property of an all wheel drive system and its actuator ishigh dynamics. Based on vehicle dynamical and traction optimizingdesired values, it shall be possible to reach the desired torque asquickly as possible. The accuracy with which this is obtained shall alsobe as high as possible without creating superimposed disturbances, i.e.overtones of any kind to the fundamental signal.

A pressure regulator and thus torque regulator of the type shown in theabove publications has basically a highly dynamic function. There is aninherent risk that it may react in a non-desirable way on processdisturbances that are caused by for example external acceleration,vibrations, temperature changes, and rotation speed variations. As aresult superimposed torque variations in a non-desired frequency rangemay occur.

It may thus be desirable to introduce control over the dynamics of theregulator in a defined frequency range in order not to be forced to makea balance between high dynamics and robustness against processdisturbances.

THE INVENTION

In a hydraulic pump assembly of the kind described above this mayaccording to the invention be attained by the introduction of a definedfriction surface between the lever and one of the radial flanges and byspring means for resiliently biasing the lever against said one of theflanges.

The friction surface is preferably in the form of a knob on an axialside of the lever.

In a first embodiment a compression spring placed in an axial bore inthe lever may be arranged to push a ball against the other radialflange.

In the known regulator there is a ring spring arranged around the pistondrum and laid over an axial pin on the lever for controlling the radialmovement of the lever. In a second embodiment of the invention the axialpin has a surface sloping downwards from the lever towards the pistondrum.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below under referenceto the accompanying drawings, in which

FIG. 1 is a hydraulic scheme for an AWD coupling in a road vehicle,

FIG. 2 is a cross section through a centrifugal regulator portion of ahydraulic pump assembly for that AWD coupling, relevant for the presentinvention,

FIG. 3 is an axial section generally through the portion shown in FIG. 2of a first embodiment of a device according to the invention,

FIG. 4 is a radial section through the first embodiment according toFIG. 3,

FIG. 5 is an axial section generally through the portion shown in FIG. 2of a second embodiment of a device according to the invention,

FIG. 6 is a radial section through the second embodiment according toFIG. 5, and

FIG. 7 is an isometric view of an exemplary lever to be used in thesecond embodiment according to FIG. 5.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1 and 2 stem from WO 2011/043722, to which reference is made for afull understanding of a hydraulic pump assembly, in which the presentinvention may be embodied. This hydraulic pump assembly is intended foruse in an actuation system for a limited slip coupling for thedistribution of torque for example in all wheel drive vehicles (AWD).

The hydraulic system shown in FIG. 1 includes an electric motor 1,driving a pump 2 via a drive shaft 3, which also drives a centrifugalregulator 4. The position of the centrifugal regulator 4 controls theposition of and flow through a pressure overflow valve 5.

Hydraulic oil for the hydraulic actuator system is contained in areservoir 6. It is sucked into the pump 2 through a hydraulic line 7 andis delivered therefrom towards a hydraulic cylinder 8 for actuating adisc package 9 of a limited slip coupling 10 by means of a piston 11 inthe cylinder 8.

Depending on the position of the centrifugal regulator 4 and thus thepressure overflow valve 5, a portion and sometimes all of the hydraulicflow is diverted through a hydraulic line 12, through the overflow valve5 and back to the reservoir 6. The result is that the hydraulic pressuredelivered to the cylinder 8 is governed by the centrifugal regulator 4.

A relief valve 13 is connected to the cylinder 8 by means of a hydraulicline 14. The relief valve 13 has the purpose of diverting hydraulic oilfrom the cylinder 8 to the reservoir 6, when its pressure exceeds acertain level, for example 40 bar.

The electric motor 1, the pump 2, the drive shaft 3, the centrifugalregulator 4, and the overflow valve 5 are included in a hydraulic pumpassembly. FIG. 2 is a cross section through members of the centrifugalregulator 4 and the overflow valve 5 in the hydraulic pump assembly.

Shown in FIG. 2 is a piston drum 20, being part of the pump 2 androtated at operation. The rotation axis of the drum 20 defines the axialdirection throughout the specification, and the direction perpendicularthereto is the radial direction. The piston drum 20 is provided withpreferably three radial bores 21 for hydraulic oil. At the peripheralend of each bore 21 there is a valve member, preferably in the form of aball 22.

For controlling the application of each ball 22 against the open end ofits bore 21 and thus the hydraulic flow past the ball 22, there is acentrifugal lever 23. The lever 23 is relatively close to a first one ofits ends pivotally attached to the piston drum 20 by means of a leverpin 24. At rotation of the piston drum 20 the other or second end of thelever 40 will be biased radially out from the piston drum 20 by thecentrifugal force. This tendency is counteracted by a spring means inthe form of a ring spring 25, laid around spring pins 26 on the levers23. The ball 22 is preferably connected to the lever end by means of aspring clip 27, which will allow the ball 22 to fit sealingly in thebore end or mouth of the bore 21.

In FIG. 2 the levers 23 are shown swung out radially under the action ofa centrifugal force, and the balls 22 are closing off the radial bores21.

For further information about the design and function of the hydraulicpump assembly, reference is made to said WO 2011/043722.

As has been explained more in detail above, the main object of theinvention is to improve the control of the dynamics of the centrifugalregulator, comprising in essence the levers 23 controlling the balls 22.

A first embodiment of a device for such an improvement is shown in FIGS.3 and 4. Shown therein are the piston drum 20, one ball 22, and onecentrifugal lever 23 with its pivot pin 24. It also appears that thepiston drum 20 is provided with radial guide flanges 20′ at a slightlylarger axial distance from each other than the width of the levers 23.These flanges 20′ were basically intended to guide the levers 23 withoutinterfering with their radial movements.

Now, according to the improvement, a certain control of the levers 23 incooperation with the drum flanges 20′ is introduced.

On one of its axial surfaces, namely its left hand surface in FIG. 3,the lever 24 is provided with a defined friction surface 28, preferablyin the form of a small knob, for cooperation with the left hand flange20′.

Generally opposite the friction surface, the lever 23 is provided with abore 29, housing a compression spring 30 and a ball 31 contacting theright hand flange 20′. The spring and ball arrangement will create anaxial force biasing the friction surface 28 into engagement with theleft hand flange 20′. There will also be a minor friction between theball 31 and the right hand flange 20′. The required axial force may beprovided by any alternative spring arrangement, as will be apparent toany person skilled in the art.

A second embodiment of a device for the improvement mentioned above isshown in FIGS. 5-7. Shown in FIG. 5 are the piston drum 20 with itsradial flanges 20′ and the centrifugal lever 23. Also shown in FIG. 5 isthe ring spring 25, mentioned above in connection with FIG. 2. Shown inFIG. 6 are the piston drum 20, the lever 23, the ring spring 25, as wellas the pivot pin or lever pin 24.

Referring to FIG. 5, also in this case the lever 23 is provided with adefined friction surface 32 on one of its axial surfaces, namely itsright hand surface. This friction surface 32 has preferably the form ofa small knob for cooperation with the right hand flange 20′.

The ring spring 25, which was present in the prior art device shown inFIG. 2, is here utilized for also providing an axial force biasing thefriction surface 28 into engagement with the right hand flange 20′. Forthis purpose the straight spring pin 26 on the lever 23 in FIG. 2 isreplaced by a sloping pin 33 with a surface sloping downwards from thelever 23 towards the piston drum 20.

As is most clearly shown in FIG. 6, the ring spring 25 is laid aroundthe lever pin 24 as well as the sloping pin 33 on each lever 23.

In the known version according to FIG. 2, the spring ring 25 creates aradial force on the lever 23, but by the use of the sloping pin 33 alsoan axial force is created acting to bias the friction surface 32 intoengagement with the right hand flange 20′. The axial force is created bythe reaction force between the ring spring 25 and the piston drum 20 asa result of the sloping surface of the pin 33 initially biasing the ringspring 25 axially against the piston drum 20.

The lever 23 is shown in FIG. 7. Shown here are a lever bore 24′ for thelever pin 24 and the sloping pin 33.

The invention is not limited to its use with a hydraulic pump assemblyexactly as shown and described in the referenced publications.

Modifications are possible within the scope of the appended claims. Thefriction surfaces may for example be arranged on the flanges instead ofon the levers.

The invention claimed is:
 1. A hydraulic pump assembly, comprising arotatable piston drum with at least one centrifugal lever pivotallyattached thereto for radial movements between radial flanges under theaction of centrifugal force at rotation of the piston drum, thecentrifugal lever being arranged to control the position of a valvemember, at the opening end of a bore in the piston drum, a definedfriction surface between the lever and one of the radial flanges, and aspring means for resiliently applying an axial force acting on a surfacelocated between the axial extents of the lever biasing the lever againstsaid one of the radial flanges.
 2. An assembly according to claim 1,wherein the friction surface is in the form of a protrusion on an axialside of the lever.
 3. A hydraulic pump assembly, comprising a rotatablepiston drum with at least one centrifugal lever pivotally attachedthereto for radial movements between radial flanges under the action ofcentrifugal force at rotation of the piston drum, the centrifugal leverbeing arranged to control the position of a valve member, at the openingend of a bore in the piston drum, a defined friction surface between thelever and one of the radial flanges and by spring means for resilientlybiasing the lever against said one of the flanges, wherein a compressionspring placed in an axial bore in the lever is arranged to push a ballagainst the other radial flange.
 4. An assembly according to claim 1,having a ring spring arranged around the piston drum and laid over anaxial pin on the lever for controlling the radial movement of the lever,wherein the axial pin has a surface sloping downwards from the levertowards the piston drum.